A calibration of the Fricke dosimeter is a measurement of epsilon G(Fe3+). Although G(Fe3+) is expected to be approximately energy independent for all low-LET radiation, existing data are not adequate to rule out the possibility of changes of a few per cent with beam quality. When a high-precision Fricke dosimeter, which has been calibrated for one particular low-LET beam quality, is used to measure the absorbed dose for another low-LET beam quality, the accuracy of the absorbed dose measurement is limited by the uncertainty in the value of G(Fe3+). The ratio of G(Fe3+) for high-energy x-rays (20 and 30 MV) to G(Fe3+) for 60Co gamma-rays, G(Fe3+)MV(Co), was measured to be 1.007(+/-0.003) (confidence level of 68%) using two different types of water calorimeter, a stirred-water calorimeter (20 MV) and a sealed-water calorimeter (20, 30 MV). This value is consistent with our calculations based on the LET dependence of G(primary products) and, as well, with published measurements and theoretical treatments of G(Fe3+).

https://iopscience.iop.org/article/10.1088/0031-9155/44/7/303/pdf

Fricke dosimetry: the difference between G(Fe3+) for 60Co gamma-rays and high-energy x-rays.

The nuclear magnetic resonance (NMR) longitudinal relaxation rate R1 dose-response characteristics of a ferrous-sulphate-doped chemical dosimeter system (Fe MRI) immobilized in a gelatin matrix were explored. Samples containing various concentrations of the FeSO4 dosimeter were irradiated to absorbed doses of 0-150 Gy. R1 relaxation rates were determined by imaging the samples at a field strength of 1.5T(1H Lamor frequency of 63.8 MHz). The response of the system was found to be approximately linear up to doses of 50 Gy for all FeSO4 concentrations studied (0.1-2.0 mM). Changing concentrations in the range of 0.1-0.5 mM affected both the slope and intercept of the dose-response curve. For concentrations of 0.5-2.0 mM, the slope of the dose-response curves remained constant at approximately 0.0423 s-1 Gy-1 in the dose range of 0-50 Gy. However, the intercept of the curve continued to increase in that region, as expected, because of the additional paramagnetic ions. The reproducibility of the absorbed dose estimates for measurements made over a 22 cm field of view was found to be 5% in the range of 20-50 Gy (an uncertainty of 0.81 Gy on average), decreasing to approximately 10% in the dose range of 5-10 Gy.

https://iopscience.iop.org/article/10.1088/0031-9155/36/8/007/pdf

Dose-response characteristics of a ferrous-sulphate-doped gelatin system for determining radiation absorbed dose distributions by magnetic resonance imaging (Fe MRI)

Radiometric calorimetry: a review

A detailed investigation of the ferrous sulfate radiation dosimeter was carried out, and $G{}_{{\rm Fe}}{}^{++}\rightarrow {}{}_{{\rm Fe}}{}^{+++}$ values were determined for a number of γ-, X-, and β-rays of a wide range of radiation energy with an overall accuracy of some ±2%. Ionization methods of estimation of absorbed radiation dose were employed for 14-MeV X-rays, Co60 γ-rays, ${\rm Cs}^{137}$ γ-rays, ${\rm Ir}^{192}$ γ-rays, 220-kVp X-rays, 100-kVp X-rays, 60-kVp X-rays, and ${\rm Y}^{90}$ β-rays; and particle counting was used for estimating the radiation energy emitted by H3, S35, and P32 β-rays. An isothermal microcalorimetric method was also used in the calibration of the H3 and P32 radioactive samples, and an adiabatic one for the absorbed dose measurement of the 14-MeV X-rays, the Co60 γ-rays, and the 220-kVp X-rays. The results obtained are in general agreement with most recently published values of other workers for corresponding radiation qualities where these have been investigated.

Calibration of the Ferrous Sulfate Dosimeter by Ionometric and Calorimetric Methods for Radiations of a Wide Range of Energy

GUPTA, B. L., BHAT, R. M., GOMATHY, K. R., AND SUSHEELA, B. Radiation Chemistry of the Ferrous Sulfate-Benzoic Acid-Xylenol Orange System. Radiat. Res. 75, 269-277 (1978). In the dosimetric system containing 0.20 mM ferrous ammonium sulfate, 5.0 mM benzoic acid, and 0.20 mM xylenol orange in 0.05 N sulfuric acid (FBX system), benzoic acid increases the G(Fe3+) value and ferric ions form a complex with xylenol orange. This paper presents the investigations carried out regarding the reactions of H202, OH, and H in the FBX system. The OH radicals were generated by the reaction of ferrous ions with H202. In the FBX system, each H202, OH, and H leads to the oxidation of 8, 7, and 11 ferrous ions, respectively. In the absence of xylenol orange, the above values respectively are 12, 11, and 13. The rate constant of the reaction of OH radical with xylenol orange in 0.05 N H2SO4 has been measured by competition kinetics using benzoic acid and its value has been found to be 7.9 X 109 M-' sec-L. In the absence of oxygen there is no radiolytic oxidation of ferrous ions in FBX system.

Radiation Chemistry of the Ferrous Sulfate-Benzoic Acid-Xylenol Orange System

The construction and operation details of a local absorbed dose microcalorimeter are presented. This calorimeter measures the absorbed dose rate at any desired point within an irradiated medium. The measurement is specific to a sufficiently limited region (2.0 cm in dia, 0.3 cm deep) that the measurement is essentially at a point and no integration or averaging process is necessary to qualify either the absorbed dose, or its rate. The system is sufficiently sensitive to provide about 1% accuracy at dose rates of 50 rads/min. The application of this calorimeter to 10-Mev and 20-Mev incident electrons is described. The use of a secondary standard (Victoreen 25-r chamber) under specified conditions is given together with details of calibration for use with high-energy electrons. The influence of the polarization effect was noted. The Fricke ferrous sulfate dosirieter was also calibrated for these energies of electrons. Samples of dosimeter solution were exposed in a geometry identical with that of the small sensitive region of the calorimeter. A value of G/sub Fe// sup 3+/ of 15.32 plus or minus 0.34 was obtained for 10-Mev electrons, and a value of 15.17 plus or minus 0.28 for 20-Mev electrons. (auth)

Calorimetric Determination of Absorbed Dose and G Fe +++ of the Fricke Dosimeter with 10-Mev and 20-Mev Electrons

>The effects of Cl/sup -/ and O/sub 2/ observed when other organic compounds were introduced into the Fricke dosimeter were also observed with a ferrous sulfate-benzoic acid system, although ferric yield was considerably more reproducible in this case than in previously tried systems, The conclusion that peroxides are formed was reinforced by the fact that ferrous ion is oxidized by benzoic acid solutions which have previously been irradiated. The production of hydroxy isomers of benzoic acid was found to occur to a greater extent in this system (G = 1.9 molecules per 100 ev; G/sub m/ = 3.1; G/sub p/ = 1.6) than in alkaline solution of benzoic acid alone as investigated by Armstrong et al. (G/ sub o/ = 0.67 molecule/ev; G/sub m/ = 0.37; G/sub p/ == 0.37), and in different ratios from those found by Armstrong (o/m/p = 9: 5: 5) or by Loebl et al., who irradiated at pH 3 and got ratios of 5: 2: 10. These discrepancies might indicate either differences in analytic technique or a fundamental difference in mechanism due to the presence of ferrous ion. (auth)

The Radiation Chemistry of Aqueous Ferrous Sulfate-Benzoic Acid Solutions

Experiments were run to determine if liquid chemical systems such as the Fricke dosimeter may be used to measure the amount of photoelectric absorption for a particular photon spectrum. Extinction coefficients of ferric ion in various solutions were determined relative to the extinction coefficient of ferric ion in 0.8N H/sub 2/SO/sub 4/. Energy absorption in solutions was calculated by graphical integration. Results in 1.6, 0.8, and 0.3N H/sub 2/SO/ sub 4/ solutions with a variety of radiations are summarized. Optical density changes produced in O.8N H/sub 2/SO/sub 4/ solutions containing added zinc and cadmium are given. These additions did not detectably change the G value for ferric ion production in the Fricke dosimeter. (M.C.G.)

Janet Geisselsoder

Papers

Calorimetric Determination of Absorbed Dose and G Fe +++ of the Fricke Dosimeter with 10-Mev and 20-Mev Electrons

The Radiation Chemistry of Aqueous Ferrous Sulfate-Benzoic Acid Solutions

Use of the Fricke Dosimeter to Measure Photoelectric Absorption